A gas turbine engine such as that used for powering an aircraft in flight includes a combustor which generates hot combustion gases, with the discharge therefrom flowing through a high pressure turbine nozzle which directs the combustion gases to a row of turbine rotor blades which extract energy therefrom for rotating a disk and shaft joined thereto for typically powering a compressor of the engine. The first stage turbine rotor blades receive the hottest combustion gases in the engine and are therefore typically hollow and provided with various structures used for providing effective cooling thereof for ensuring useful operating lives therefor.
The turbine rotor blades typically include serpentine flow passages therein and various cooling holes through the airfoil pressure side, suction side, or tip as required. Cooling air is provided to the blade by bleeding a portion of relatively cool compressor air and suitably channeling it through the blade dovetail and into the blade for supplying the cooling structures therein. However, any air bled from the compressor which is used for cooling purposes is not therefore used in the combustion process which necessarily decreases the overall efficiency of the engine. It is therefore desirable to use as little as possible of compressor bleed flow for cooling purposes.
It is known that the combustion gases channeled over the turbine blades have a generally center peaked temperature profile between the roots and tips of the blades. It has recently been discovered in accordance with the present invention that secondary fluid flow patterns distort the temperature distribution over the blade airfoil resulting in a hotter gas temperature at the midchord region of the blade tip than that experienced at the leading edge on the blade pressure side. Accordingly, it is desirable to reduce the adverse heating effects of the combustion gases at turbine blade tips for reducing the cooling air requirements which would otherwise be required in the blade.